1. Field of the Invention
This invention relates to a method for the decomposition of a Michael type adduct of acrylic acid and/or an acrylic ester and more particularly to a method for the decomposition of a Michael type adduct by-produced by the action of heat or a catalyst during the production of acrylic acid and/or an acrylic ester, which method is characterized by decomposing of the Michael type adduct into acrylic acid and/or an acrylic ester and/or an alcohol in the presence of a copper salt and an alkali metal salt or an alkaline earth metal salt.
2. Description of the Related Art
Generally, the production of acrylic acid and an ester thereof, while in process, possibly entails by-production of a Michael type adduct having a carboxylic acid or an alcohol added to the carbon-carbon double bond of acrylic acid or an acrylic ester owing to the action of heat or a catalyst. The Michael type adducts thus derived include polymers of a multiplicity in the approximate range of 2-5 of molecules of acrylic acid, esters thereof, alkoxypropionic acids, and alkoxypropionic esters, for example.
If the quantity of a Michael type adduct to be by-produced increases, this increase will result in lowering the efficiency of raw material and increasing the cost of production in the process for the production of acrylic acid. This situation is unfavorable. If the Michael adduct accumulates during the process, the accumulation will seriously hinder the step of purification and the step of production. Further, the occurrence of a by-product and the elevation of temperature will degrade the quality of the product. The practice of concentrating the Michael type adduct at the step of purification, discharging the concentrate out of the process system, and disposing of it by incineration is generally followed. This incineration, however, is unfavorable even from the viewpoint of the environmental preservation. In the process for the production of acrylic acid, efforts have been made to decompose the Michael type adduct and reclaim the product of this decomposition.
As a way of decomposing such a Michael type adduct, for example, a method which decomposes an oligomer of acrylic acid or an acrylic ester, an alkoxypropionic acid, or an alkoxypropionic ester by the action of heat or a catalyst has been known. Specifically, U.S. Pat. No. 3,868,410 discloses a method which decomposes a Michael type adduct by-produced during the esterification of acrylic acid with an alcohol into monomers by heating the adduct at a temperature of 180° C. or more. Then, U.S. Pat. No. 3,639,466 discloses a method which produces acrylic acid by heating the residue occurring in the finishing step of acrylic acid in the presence of a compound possessing a primary or tertiary amino group or in the presence of a tertiary phosphine as a catalyst.
These methods in operation, however, require fairly high temperatures and recover acrylic acid only with low percentages. When they are compelled to obtain acrylic acid with high recovery percentages, they encourage secondary reactions and yield large quantities of such by-products as high-boiling substances and low-boiling substances which degrade the quality of acrylic acid or an acrylic ester. After all, these methods do not easily recover acrylic acid with a high percentage.
Further, the JP-A-03-178949 discloses a method for recovering monomers from the Michael type adduct by-produced in the production of acrylic acid and an ester thereof by catalytically decomposing this adduct in the presence of a solid acid at an elevated temperature of 200° C. or more. By this method, the Michael type adduct is decomposed with a high percentage. This method, however, is unfavorable from the viewpoint of the quality of the product because the reaction proceeds at the elevated temperature and forms by-products such as low-boiling substances with high percentages. Since the decomposition proceeds in the form of a solid-liquid reaction, the catalytic activity is markedly degraded by poisoning. Furthermore, since the methods described above invariably concern reactions at elevated temperatures, they are fated to form highly viscous residues which will eventually solidify after a protracted retention. Thus, they are at a disadvantage in rendering the disposal of their residues very difficult.
Chinese Patent 1046324A discloses a method for recovering acrylic acid from a waste liquid containing acrylic acid and a dimer of acrylic acid by heating this waste liquid together with the process water, and following destructive distillation. This method aims to lower the viscosity of the waste liquid by the addition of the process water and facilitate the distillation of acrylic acid and the dimer of acrylic acid. The method of Chinese Patent 1046324A, however, has the problem that the thermal treatment of high temperature in the presence of water gives rise to polymers like polymer of acrylic acid, adds to the viscosity of there action solution, and aggravates adverse behaviors of the reaction solution as by gelation. Further, since the used process water must be isolated from the system, the manufacturing process will be complicated.
The JP-A-57-62229 discloses a method which consists in treating heavy substances by-produced during the production of an acrylic ester with an aqueous alkali solution. This method, however, forms a precipitate due to the treatment with the aqueous alkali solution and forms polymers such as polymer of acrylic acid due to the heat of neutralization. It, therefore, entails such problems as aggravating the condition of the reaction solution by thickening or gelation, and the problem caused disadvantage from the viewpoint of energy. Moreover, this method poses the problem of impairing the quality of the product owing to the by-products like β-hydroxy propionic acid.
In the circumstance, the development of a technique which is capable of converting the Michael type adduct into at least one compound selected from the group consisting of useful acrylic acid, esters thereof and alcohols, and recovering or reclaiming or reclaiming this useful compound efficiently has been being craved.